1/*
2 * Copyright © 2014 Intel Corporation
3 *
4 * Permission is hereby granted, free of charge, to any person obtaining a
5 * copy of this software and associated documentation files (the "Software"),
6 * to deal in the Software without restriction, including without limitation
7 * the rights to use, copy, modify, merge, publish, distribute, sublicense,
8 * and/or sell copies of the Software, and to permit persons to whom the
9 * Software is furnished to do so, subject to the following conditions:
10 *
11 * The above copyright notice and this permission notice (including the next
12 * paragraph) shall be included in all copies or substantial portions of the
13 * Software.
14 *
15 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
16 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
17 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.  IN NO EVENT SHALL
18 * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
19 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
20 * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS
21 * IN THE SOFTWARE.
22 *
23 * Authors:
24 *    Jason Ekstrand (jason@jlekstrand.net)
25 *
26 */
27
28#include "nir_constant_expressions.h"
29#include <math.h>
30
31/*
32 * Implements SSA-based constant folding.
33 */
34
35struct constant_fold_state {
36   void *mem_ctx;
37   nir_function_impl *impl;
38   bool progress;
39};
40
41static bool
42constant_fold_alu_instr(nir_alu_instr *instr, void *mem_ctx)
43{
44   nir_const_value src[NIR_MAX_VEC_COMPONENTS][NIR_MAX_VEC_COMPONENTS];
45
46   if (!instr->dest.dest.is_ssa)
47      return false;
48
49   /* In the case that any outputs/inputs have unsized types, then we need to
50    * guess the bit-size. In this case, the validator ensures that all
51    * bit-sizes match so we can just take the bit-size from first
52    * output/input with an unsized type. If all the outputs/inputs are sized
53    * then we don't need to guess the bit-size at all because the code we
54    * generate for constant opcodes in this case already knows the sizes of
55    * the types involved and does not need the provided bit-size for anything
56    * (although it still requires to receive a valid bit-size).
57    */
58   unsigned bit_size = 0;
59   if (!nir_alu_type_get_type_size(nir_op_infos[instr->op].output_type))
60      bit_size = instr->dest.dest.ssa.bit_size;
61
62   for (unsigned i = 0; i < nir_op_infos[instr->op].num_inputs; i++) {
63      if (!instr->src[i].src.is_ssa)
64         return false;
65
66      if (bit_size == 0 &&
67          !nir_alu_type_get_type_size(nir_op_infos[instr->op].input_types[i]))
68         bit_size = instr->src[i].src.ssa->bit_size;
69
70      nir_instr *src_instr = instr->src[i].src.ssa->parent_instr;
71
72      if (src_instr->type != nir_instr_type_load_const)
73         return false;
74      nir_load_const_instr* load_const = nir_instr_as_load_const(src_instr);
75
76      for (unsigned j = 0; j < nir_ssa_alu_instr_src_components(instr, i);
77           j++) {
78         src[i][j] = load_const->value[instr->src[i].swizzle[j]];
79      }
80
81      /* We shouldn't have any source modifiers in the optimization loop. */
82      assert(!instr->src[i].abs && !instr->src[i].negate);
83   }
84
85   if (bit_size == 0)
86      bit_size = 32;
87
88   /* We shouldn't have any saturate modifiers in the optimization loop. */
89   assert(!instr->dest.saturate);
90
91   nir_const_value dest[NIR_MAX_VEC_COMPONENTS];
92   nir_const_value *srcs[NIR_MAX_VEC_COMPONENTS];
93   memset(dest, 0, sizeof(dest));
94   for (unsigned i = 0; i < nir_op_infos[instr->op].num_inputs; ++i)
95      srcs[i] = src[i];
96   nir_eval_const_opcode(instr->op, dest, instr->dest.dest.ssa.num_components,
97                         bit_size, srcs);
98
99   nir_load_const_instr *new_instr =
100      nir_load_const_instr_create(mem_ctx,
101                                  instr->dest.dest.ssa.num_components,
102                                  instr->dest.dest.ssa.bit_size);
103
104   memcpy(new_instr->value, dest, sizeof(*new_instr->value) * new_instr->def.num_components);
105
106   nir_instr_insert_before(&instr->instr, &new_instr->instr);
107
108   nir_ssa_def_rewrite_uses(&instr->dest.dest.ssa,
109                            nir_src_for_ssa(&new_instr->def));
110
111   nir_instr_remove(&instr->instr);
112   ralloc_free(instr);
113
114   return true;
115}
116
117static bool
118constant_fold_intrinsic_instr(nir_intrinsic_instr *instr)
119{
120   bool progress = false;
121
122   if (instr->intrinsic == nir_intrinsic_discard_if &&
123       nir_src_is_const(instr->src[0])) {
124      if (nir_src_as_bool(instr->src[0])) {
125         /* This method of getting a nir_shader * from a nir_instr is
126          * admittedly gross, but given the rarity of hitting this case I think
127          * it's preferable to plumbing an otherwise unused nir_shader *
128          * parameter through four functions to get here.
129          */
130         nir_cf_node *cf_node = &instr->instr.block->cf_node;
131         nir_function_impl *impl = nir_cf_node_get_function(cf_node);
132         nir_shader *shader = impl->function->shader;
133
134         nir_intrinsic_instr *discard =
135            nir_intrinsic_instr_create(shader, nir_intrinsic_discard);
136         nir_instr_insert_before(&instr->instr, &discard->instr);
137         nir_instr_remove(&instr->instr);
138         progress = true;
139      } else {
140         /* We're not discarding, just delete the instruction */
141         nir_instr_remove(&instr->instr);
142         progress = true;
143      }
144   }
145
146   return progress;
147}
148
149static bool
150constant_fold_block(nir_block *block, void *mem_ctx)
151{
152   bool progress = false;
153
154   nir_foreach_instr_safe(instr, block) {
155      switch (instr->type) {
156      case nir_instr_type_alu:
157         progress |= constant_fold_alu_instr(nir_instr_as_alu(instr), mem_ctx);
158         break;
159      case nir_instr_type_intrinsic:
160         progress |=
161            constant_fold_intrinsic_instr(nir_instr_as_intrinsic(instr));
162         break;
163      default:
164         /* Don't know how to constant fold */
165         break;
166      }
167   }
168
169   return progress;
170}
171
172static bool
173nir_opt_constant_folding_impl(nir_function_impl *impl)
174{
175   void *mem_ctx = ralloc_parent(impl);
176   bool progress = false;
177
178   nir_foreach_block(block, impl) {
179      progress |= constant_fold_block(block, mem_ctx);
180   }
181
182   if (progress) {
183      nir_metadata_preserve(impl, nir_metadata_block_index |
184                                  nir_metadata_dominance);
185   } else {
186#ifndef NDEBUG
187      impl->valid_metadata &= ~nir_metadata_not_properly_reset;
188#endif
189   }
190
191   return progress;
192}
193
194bool
195nir_opt_constant_folding(nir_shader *shader)
196{
197   bool progress = false;
198
199   nir_foreach_function(function, shader) {
200      if (function->impl)
201         progress |= nir_opt_constant_folding_impl(function->impl);
202   }
203
204   return progress;
205}
206